Some imaging device such as a digital camera comprises a shake correcting system in order to prevent a blur in an image due to camera shakes and generate a clear image. Such a shake correcting system has to be compact in size for preventing an increase in size of the imaging device in which it is mounted. Also, it has to be driven by a small power as much as possible so as to reduce consumption of electric batteries.
There are two types of shake correcting systems, one correcting a camera shake by moving a correction lens and the other by moving an image sensor. Japanese Patent No. 3969927 (Reference 1) discloses a shake correcting system with a correction lens which comprises a movable element holding the lens, a fixed element restricting movement of the movable element in an optical axis direction, three balls placed between the movable element and the fixed element and relatively movable to the movable element and the fixed element, at least three restrictors provided for the three balls respectively, and a driver driving the movable element. The at least three restrictors are provided in the movable element or the fixed element to adjust the relative positions of the three balls to be within predetermined ranges. The predetermined ranges are set to be such values that the balls are not to hit the restrictors when they move by a half of the maximum mechanical movable amount of the movable element from the center of the ranges or a half of the maximum moving amount of the movable element for a camera shake correction.
Japanese Laid-open Patent Publication No. 2006-350157 (Reference 2) discloses a shake correcting system which comprises a correction lens, a movable element holding the lens, a guide element which limits movement of the movable element to a base in the optical axis direction and guides the movable element to move in a plane orthogonal to the optical axis, a rotation restrictor which restricts rotation of the movable element around the optical axis. Reference 2 aims to downsize the shake correcting system by disposing the rotation restrictor and the guide element so that a part of the rotation restrictor and the guide element overlap in the optical axis direction.
The invention disclosed in Reference 1 has a disadvantage in an increase in the size of the corrector in the optical axis direction because the elements are arranged outwardly in a radial direction around the optical axis. The invention disclosed in Reference 2 can reduce the size thereof in the optical axis direction by the overlapping arrangement of the rotation restrictor and guide element, however, it is still disadvantageous in increasing thickness of the corrector in the optical axis direction.
Japanese Laid-open Patent Publication No. 2008-77047 discloses a shake correcting system correcting camera shakes by moving the image sensor which comprises a first movable frame with a first guide and on which the image sensor is mounted, a second movable frame having a first guide shaft and a second guide contacting with the first guide to movably support the first movable frame, and a fixed frame having a second guide shaft contacting with the second guide to movably support the second movable frame. The first guide shaft is made of a magnetic material and the first movable frame includes, on the first guide shaft, a permanent magnet which biases the first movable frame in such a direction as to make the first guide and the first guide shaft contact with each other. The magnetic force of the permanent magnet can prevent the guides from wobbling.
In the invention in Reference 3 the movable frame can be moved smoothly since the guide shaft and the movable frame are constantly in contact with each other by the magnetic force. However, it is necessary to generate a large magnetic force enough to overcome the own weight of the moving elements including the image sensor in order to prevent them from wobbling. Because of this, it has a disadvantage that friction resistance between the guide shafts and the movable frames are increased.